1. Field of the Invention
The invention concerns a method of measuring the loading of a washing drum of a washing machine or a washer-drier.
In order to optimise the washing or drying procedure, it is advantageous if the electronic control system of the washing machine or the washer-drier detects the respective loading of the washing drum. For it is then possible for procedural parameters such as water filling, supply of washing agent, speeds of rotation and timed switching operations to be matched to the respective loading. That makes it possible to achieve savings, with optimum washing results.
When the washing drum is rotating, frictional phenomena occur in the drum suspension system and the friction dampers, by virtue of a possible unbalance in terms of laundry distribution. Besides bearing friction, additional coefficients of friction also occur as a consequence of the formation of foam or other influences, for example age-induced wear phenomena. Those phenomena are referred to as xe2x80x9cmachine frictionxe2x80x9d. The machine friction can fluctuate greatly from one machine to another and under the effect of ageing. If machine friction is used to measure the drum loading, it is then to be reckoned that the measurement results will be inaccurate.
2. Discussion of the Prior Art
DE 44 31 846 A1 describes a method of the kind set forth in the opening part of this specification, in which machine friction is not to have a substantial effect on drum loading measurement. In the case of a loaded washing drum which is rotating at least at the speed causing the laundry to bear against the drum surface, the torque to be applied to maintain a constant speed of rotation by the motor of the washing drum is firstly measured. Then, the torque which occurs upon acceleration of the washing drum is ascertained. On the basis of those two torque values, the electronic control system determines the loading of the washing drum and forms a control parameter for further control of the washing machine or the washer-drier. Water is inevitably removed from the laundry during the procedures for measuring the torque at a constant speed of rotation and during measurement of the torque in the acceleration phase, and that has the consequence that the moments of inertia change during the measurement procedure. That adversely influences the measurement result. In addition, the gradient of the increase in speed of rotation in the acceleration measurement phase must be limited in an upward direction, with wet laundry, because, if the increase in speed of rotation is excessively fast, water is removed from the laundry so rapidly that in addition frictional torques which negatively influence the measurement would occur.
DE 34 16 639 A1 describes a method of controlling the spin program of a washing machine. An acceleration phase which is predetermined in the spin program involves measurement of the unbalance and the time required for the acceleration range. In this case also the above-indicated measurement inaccuracies occur.
DE 40 38 178 A1 describes a method of unbalance measurement. The mass inertia of the washing drum is measured during a slowing-down phase of the washing drum. During the slowing-down phase, only the machine friction which, as stated above, can fluctuate greatly from one machine to another and due to the effects of ageing acts so that it is scarcely possible to deduce an accurate value for the loading of the washing drum, from the variation in the speed of rotation in the slowing-down phase.
The object of the invention is to provide a method of the kind set forth in the opening part of this specification, which affords measurement results that are as accurate as possible, in particular by virtue of the fact that the removal of water from the laundry and machine friction are involved in the measurement result to the minimum possible degree.
In accordance with the invention that object is attained by the features of the characterising portion of claim 1.
In this procedure measurement is implemented while the washing drum is being actively braked by the motor. No substantial removal of water from the laundry occurs in the phase involving deceleration of the washing drum so that the water-removal effect which can only be defined with difficulty also has no action on the measurement result. As the measurement procedure is based on active braking of the motor with a detectable braking moment, the machine friction which is governed by loading and which varies from one machine to another and which is affected by ageing phenomena does not have a substantial effect on measurement. Preferably in this case the braking moment applied by electrical braking of the motor is substantially greater than the moment of the machine friction.